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Old June 12th, 2005, 08:29 PM   #1
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GG ok, but camera has light loss? Anyone experience this?

I have a nice little setup with my new Achromat that I got from a slide projector - looks great. So tonight I went to do some night test shots - looked through the DOF machine without the DV camera and saw a nice shot, crisp, night time shot, still lots of details -BUT when I stuck my miniDV (pana DV PV852) in front of it and watched the results filtered through the camera, it was really really dark, and all of the details I saw without the camera were quite literaly, gone.
This is seen in the viewfinder and the LCD - I am not sure why and I don't think it is a LUX issue, because if I take the camera and point it in the same direction without the DOF machine ,it is really bright and crisp. Something is happening between the camera and the achromat and the GG! Any ideas?

http://dvstuff.250free.com

Still struggling with hotspot issues as well that are not evident when looking directly at the GG, only with the camera placed in front (as evidenced in the shots)
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Old June 12th, 2005, 09:09 PM   #2
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its because you are losing light through your adapter. you lose approx. 2 stops with a 35mm adapter usually.
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Old June 12th, 2005, 09:13 PM   #3
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No, that is the problem - when I look at the GG through the adapter (without the DV camera), it is brighter and more detailed, then when I look at the GG with the camera - do you know what I mean? Using my naked eye, I can see lots of details in the GG, then I place the camera in front of the GG and the light loss occurs!
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Old June 12th, 2005, 09:27 PM   #4
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Did you check and make sure you didn't accidentally set your shutter speed higher? I know I've experimented with shutter speeds when testing moving adaptors, so it could be easy to turn your camera on and assume its at a slow speed.

I know I did this the other day and felt really silly after hours of struggling with lights wondering why everything was so rediculously dark.
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Old June 12th, 2005, 09:49 PM   #5
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Thought of that too - shutter speed is at 1/60 (it is as low as it will go - don't have 1/30 shutter speed).

I am wondering if I should try my old VHS-C camera to see if it is my camera doing something stupid because I can't figure out why it is acting up like that - if you look at my shots http://dvstuff.250free.com , before putting a camera in front of the acromat, I could see all the details in the house and the trees - after putting the camera in front, you see what you see in the pictures!
I am thinking that I might be cursed by the ancients of optics because everyone else seems to be sailing along smoothly and yet, the gods hold me back! Why, I say! Why?!
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Old June 12th, 2005, 10:04 PM   #6
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What you're experiencing is totally normal. The human eye is extremely sensetive to light and very quick to adjust. I think what you're seeing is true of all 35mm adapters. The human eye is unreliable for judging exposure, color temperature, etc. unfortunately because it's just so good.
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Old June 12th, 2005, 10:06 PM   #7
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Where'd you get a good achromat, by the way? My ebay macro lens sucks and I need a replacement.
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Old June 13th, 2005, 03:29 AM   #8
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Naked human eye is extremely sensitive... thats all. Chip in your camera is not sensitive as your eye, so the chip can not see such small light as your eye can. This is normal and right...
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Old June 13th, 2005, 05:50 AM   #9
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Daves,

Lets face it. F1.0 lens will not lose any light. You only have adapter loss. Put in F1.4 and you lose one stop, plus proabably one stop lost in adapter. Put on F2.8 lens, you lose 4 stops. Another problem is camera with adapter is at telephoto, which means another 1-2 stiops loss compared to wide and normal zoom range.

My suggestion to shoot with adapter in not well lit room and note what F stop 35 mm and camera lenses are. Then shoot without adapter. Check how the lens max opening changed for same field of view, without adapter. It may be 1-2 stops.

Then close iris until you get same low light performance as with adapter. Check lens F-stop.

Then let us please know what you found.

Radek
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Old June 13th, 2005, 06:43 AM   #10
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Quote:
Originally Posted by Daves Spi
Naked human eye is extremely sensitive... thats all. Chip in your camera is not sensitive as your eye, so the chip can not see such small light as your eye can. This is normal and right...
You mean its me peepers not me camera?
Well that is a relief. I am going to try with a different lens and see what I get!
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Old June 13th, 2005, 06:44 AM   #11
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I'm not using camera on telephoto and I have no more optical things except Primary lens, GG and Camera. My primary lens have F4, which is bad, but camera is working at F1.6. Anyway, I do not care how much I am loosing F-stops. Numbers are just numbers. Important is, that on two meters I can shine up mans face enough to shoot on Gain 0 with 30W light at midnight. During the day, I have to set shutter speed to 100, or start using iris on primary lens...

but to stay on topic...

The thing touched by Mandy is right. Because of using adapter, you will get some light loss. And even if you can see nice image through your naked eye on GG (because you eye is sooooo sensitive), you can not see the same thing with camera. Because the chip inside is not so sensitive and you add some ~2F by camera optics and some loss by macro or whatever... Its similar to hotspot thing. If you look at GG, you see nice image. But when look through camera, you will get vignetting...
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Old June 13th, 2005, 04:29 PM   #12
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Thanks Dave! I can see the difference with or without the achromat. And yes, Dave, you are right! Without the camera, there is no vignetting or hotspots, with the camera, all of the above! How do I fix this problem? Get a better camera? I am not sure right now, but at least I am not crazy. I wonder how Matthew Kent is doing it, he seems to be speeding along!
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